The volume of fresh water being used to fracture oil and gas wells is of growing concern to operating companies because it is a significant expense that involves purchase, transportation, onsite storage, heating, chemical additives, and post-treatment disposal. Reducing frac water volumes is important to reducing the environmental impact and improving the economics of multistage completions.
Current multistage methods include plug-and-perf and ball-drop frac sleeves. Both of these methods bullhead frac fluids and sand down the casing and consume large quantities of water. In recent years, fracturing techniques using coiled tubing have dramatically reduced the amount of frac water required while delivering equivalent or superior results. These techniques combine coiled tubing with sliding sleeves and resettable frac isolation. The coiled tubing provides a means of circulating fluids to the frac zone, as opposed to bullheading, and enables the sliding sleeves to be shifted mechanically without using pump-down balls.
When the frac is pumped down the annulus between the casing and coiled tubing (annular fracturing), water use is reduced by as much as 20% compared to methods that do not use coiled tubing during the fracturing process. For many multistage completions, water volume can be reduced up to 50% by pumping frac fluids through the coiled tubing. This paper describes these systems and their deployment and includes a case history describing how one operator reduced water use significantly through the application of this method without compromising treatment volumes or stimulation design parameters, while still achieving all of the original completion objectives.